1. Field of the Invention
The present invention relates generally to methods and apparatus for the thermal ablation of hollow body organs, such as the gallbladder. In particular, the present invention relates to a catheter structure having a suspended heating element at its distal end and a method for inducing an oscillating flow of a heat transfer fluid past the heating element to enhance heat transfer to and temperature uniformity throughout the transfer medium.
In recent years, a variety of "minimally invasive" surgical procedures has been developed as alternatives to conventional "open" surgery. While minimally invasive surgical procedures have no fixed definition, they are generally characterized by use of specialized surgical tools in combination with visual or radiographic imaging techniques. The specialized tool is generally inserted through an open body orifice or a small surgical incision, and the tool is then positioned within the body using the imaging technique to allow manipulation of the organ or structure to be treated. A common example of least-invasive surgery is arthroscopic knee surgery, where penetration of the surgical tools is minimal. Less-accessible body organs, such as the heart and interior blood vessels, may be reached by specialized catheters which may be routed through the vascular system over relatively long distances. Exemplary of such vascular catheters are balloon dilatation catheters which are used to expand regions of stenosis within diseased blood vessels.
Of particular interest to the present invention are least-invasive surgical techniques which rely on a catheter to deliver heat to the interior of a hollow body organ. As described in detail in co-pending applications Ser. Nos. 07/407,839; 07/529,077; and 07/551,971, the delivery of heat maybe used for deactivating or ablating a diseased body organ, such as a gallbladder, appendix, uterus, kidney, or the like, as well as for blocking other body lumens, such as blood vessels. In each case, the heat is usually delivered by conduction through a thermal conduction medium from a heating element disposed in the organ or blood vessel. The heat destroys the mucosa or endothelial lining of the organ or vessel, resulting eventually in deactivation and eventual resorption of the organ or vessel.
The use of catheters having heating elements to deliver heat within a hollow body organ can be problematic in certain respects. First, heat distribution through the thermally conductive medium can be non-uniform, requiring an increase in the total amount of heat delivered in order to assure that the temperature of all portions of the mucosa are raised above the threshold level necessary to induce injury and necrosis. Such an increase in heat delivery, however, may raise the temperature of the other portions of the mucosa above a desired maximum. Such excessive heating can result in injury to adjacent body organs. A related difficulty arises from the limited heat transfer capacity of the thermally-conductive medium. In order to deliver sufficient heat to remote portions of the mucosal wall, it may be necessary to raise the surface temperature of the heating element above a desired maximum. Excessively hot heating surfaces can result in fouling of the heating element as a result of coagulation and denaturing of blood and other proteins present. Such fouling, of course, further reduces the heat transfer capacity of the heating element.
For these reasons, it would be desirable to provide improved methods and apparatus for delivering heat to the interior of hollow body organs. It would be particularly desirable to provide thermal ablation catheters having improved heat transfer characteristics so that the surface temperature of a heating element can be maintained below a desired maximum level, typically being below about 100.degree. C., preferably being below about 90.degree. C. The methods and apparatus should further provide for improved uniformity of heat distribution throughout the thermally conductive medium used to transfer heat from the catheter to the mucosal lining of the hollow body organ. Such improved heat transfer should even further reduce the surface temperature of the heating element as well as reducing the total amount of heat delivered to the body organ. The reduction in total heat will reduce the likelihood of unintentionally injuring adjacent body organs. The catheters of the present invention should have few or no moving parts and should be simple and reliable in design.
2. Description of the Background Art
U.S. Pat. No. 4,160,455, describes a bidirectional pump and unidirectional valve means for circulating a fluid through a housing containing a heating element. The entire housing is placed within a body cavity for effecting heat treatment of tumors. The device relies on forming a single high-speed outlet jet to agitate the fluid content of the organ. U.S. Pat. No. 4,979,948, describes a device having a radio frequency balloon electrode at its distal end for thermally destroying the mucosal layer of a body organ, such as the gallbladder. U.S. Pat. Nos. 4,655,744; 4,723,941; 4,755,167; 4,758,596; 4,793,776; and Australian published application A-71786/87, describe improved methods for performing chemical cholecystectomy where a stone dissolving agent is oscillated in and out of a body area.
Coleman, Non-Surgical Ablation of the Gallbladder, Proc. 1988 SCVIR, pp 214-219, is a review article discussing various techniques for non-surgical gallbladder ablation, including the work of Salomonowitz and of Getrajdman relating to the introduction of an externally heated medium to induce fibrosis of the gallbladder. The article further presents data demonstrating thermal ablation of a dog's gallbladder after open surgical injection of hot contrast media. The work of Salomonowitz is described in Salomonowitz et al. (1984) Arch. Surg. 119:725-729. The work of Getrajdman is described in Getrajdman et al. (1985) Invest. Radiol. 20:393-398 and Getrajdman et al. (1986) Invest. Radiol. 21:400-403. The use of sclerosing agents to induce gallbladder fibrosis is described in Remley et al. (1986) Invest. Radiol. 21:396-399. See also Becker et al. (1988) Radiology 167:63-68; Becker et al. (1989) Radiology 171:235-240; and Becker et al. (1989) Work in Progress Paper #1354, RSNA Meeting, November 1989. U.S. Pat. No. 4,160,455, describes a device for internally heating a body cavity for therapy, where the heat is intended to inhibit the growth of tumor cells. German Patent 37 25 691 describes a catheter combining a heater at its distal tip and a balloon proximate the heater, where the heater is not directly exposed to the fluid environment surrounding the catheter tip. U.S. Pat. No. 4,869,248, describes a thermal ablation catheter having a resistive heating loop at its distal end. Other patent documents describing heated or cooled catheters include U.S. Pat. Nos. 4,676,258; 4,638,436; 4,469,103; 4,375,220; 3,901,224; USSR 1329-781-A; and USSR 281489.
The subject matter of the present application is related to that of co-pending application Ser. Nos. 07/407,839; 07/529,077; and 07/551,971, assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference.